Lact 14 Flashcards
Crocodylia within Amniota
In archosauria
Which is in sauropsida
Which is in amniota
Archosauria is sister group to lepidosauria
Characters of Crocodylia
• Integumentary sensory organs – sensitive mechanoreceptors (develop in skin, location varies by order)
• Respiration driven by hepatic piston
- Hepatic refers to the liver
- Muscles draw the liver backward to expand thoracic cavity
(Which increases Vol of Thoracic cavity, air comes in, increases pressure of back cavity tho. Some muscles involved in respiration)
• Body covered by keratinized non-overlapping scutes
- Some scutes supported by an osteoderm: a type of dermal bone (bony component. Centres of mineralization from within dermis, provide protection)
Scutes are larger than the scales areound them,
Relationships within Crocodylia
Alligatoridae
(Alligator, Caiman, melanosuchus, paleosuchus)
Most distal group
Crocdylidae (true crocs)
(Crocodylus, mecistops, osteolaemus)
More closely related to Gavialidae
Gavialidae (most derived)
2 groups
1st
(Tomistoma, schleglii)
2nd
(Gavialidae, gangeticus)
Croc and Gav more closesly related to each other than either are to All
Alligatoridae
• Blunt, U-shaped snout
• Only upper teeth are visible when the mouth is closed (upper jaw wide/bigger than lower jaw)
• Integumentary sensory glands only located on the head
• Found in China and the Americas
Crocodylidae
Most diverse group
• Tapering snout
• Upper and lower teeth visible when mouth is closed (upper and lower jaws are roughly same size. More tight bite. Tooth row not completely straight)
• Integumentary sensory glands distributed across head and body
• Salt glands on tongue (b/c live in saltwater. Help homeostasis. Excrete salt)
• Found in tropics and subtropics of Africa, Asia, Australia, and the Americas (widest distribution)
Gavialidae
• Strongly constricted snout
• Upper and lower teeth visible when mouth is closed (narrow jaws, tooth row straight)
• Integumentary sensory glands distributed over head and body
• Found in India and southern Asia and surrounding island groups
Bite force weak due to specializing in hunting fish and smaller prey items
Locomotion
Swimming
• Lateral undulations of the tail
• Hindlimbs help with steering
All capable of swimming
Compressed side to side tail, tail gets taller —> better propulsion
Locomotion
High walk
• Limbs under the body (upright posture) and body off the ground
• Slow, but greater endurance
Ones that spend more time on land
Bones are taking more of the weight, for longer distance travel
Locomotion
Belly crawl
• Limbs extend to the sides (sprawling posture), body and tail drag along the ground
• Can run like this (short burst, not for ,long distance)
Used for ambushing prey
Locomotion
Gallop
• Limbs under the body (up right position) and move as pairs
• Can reach 17 km/h, but only for short distances
• Only seen in Crocodylidae
Sometimes for prey or avoiding danger
Metabolism is lower than mammals so don’t have the ability to run for long b/c not enough energy can be produced
Feeding
Teeth
• Conical (same shape), set it sockets
• Continuously replaced as new teeth grow within jaws
• Some variation between front and back of jaws (additional strength to hold onto prey. Teeth don’t contribute to bite force)
Jaws
• Large posterior process for attachment of jaw-closing muscles
(For large prey. Strong bite force keep pay in mouth)
Handle bony, for muscle attachment. Also muscle on head help open jaw.
Integumentary sensory organs
• Dense network of highly sensitive mechanoreceptors (grow in skin) (pressure around them, esp in water)
• Located on the head in Alligatoridae and on the head and across the body in Crocodylidae and Gavialidae
• Different developmental origin and specific function, but similar purpose as lateral line of fish
Locate prey or other members of species
Little bumps on skin
Tool use
• Two species (that aren’t closely related) have been seen to use bait to catch wading birds
• During nesting season, crocs will gather sticks and balance them across their snouts (or backs. Drift up to bank and wait)
• Try to grab birds that come to take the sticks
Seems to be learned
Communication
Sound is key
• Sound travels farther through or across water
• Habitats often have murky water or dense vegetation
Crocodiles make sounds by:
• Slapping water with head or tail
• Bellows or roars (150 meters)
• Subsonic vibrations (vibrate parts of body, transmit through water as far as 1 kilometre)
Reproduction
• Some species collect in groups and establish a hierarchy before mating
• All species are oviparous and lay hard-shelled eggs
• Some build nests above ground, some dig nests
If in water will drown tho
Reproduction: sex determination
• No genetic determination of sex
• Type II environmental sex determination (highest and lowest temps = females, middle = males)
• Most nests have enough internal temperature variation to produce offspring of both sexes
Reproduction: parental care
• Parental care is extensive
• Females defend nests, males of some species contribute
• Vocalizations are key again, from the time the young start to hatch
• Young from multiple parents form a crèche that is guarded by multiple adults
- Young remain in crèche up to three years (could be 1 year tho)
Crocodile conservation
• Threatened by habitat loss or alteration
• Wetlands are particularly subject to destruction
• Introduced species prey on eggs and juveniles
Crocodiles in different habitats
• Most crocodiles today are semi-aquatic
- Require aspects of both terrestrial and aquatic habitats to survive and complete their life cycle
• During the Mesozoic, crocodiles filled a much greater variety of niches
• Based on what you have learned, consider how crocodile morphologies and behaviours would differ for:
- Fully aquatic species
- Fully terrestrial species
Key Concepts
• There are three clades of crocodylians, united by integumentary sensory glands and scutes covering body.
• Crocodiles depend on sound for communication in their habitats where lines of sight are often obscured.
• Crocodiles are oviparous, with environmental sex determination, and extensive parental care.
• The crocodile lineage used to be significantly more diverse, and species of extinct crocodiles filled many more niches than the semi- aquatic carnivores seen today.
